1. Field of the Invention
The invention relates to a method for the production of a vacuum insulation element wrapped in a film and filled with powder.
Using evacuated insulation materials, it is possible to achieve thermal conductivity levels that are lower by a factor of five to twenty than those possible with ventilated, conventional insulators. It is possible, for example, to produce very compact, highly insulating transport containers for temperature-sensitive goods or to realize extremely slim insulation structures in the construction field.
2. Description of the Prior Art
Pressure-resistant materials suitable for the core of evacuated insulation panels are generally available in panel form for better handling. These panels are usually pressed out of powder or cut from a pressed sheet and are commonly wrapped in an air-permeable nonwoven polyester fabric to reduce dust formation. This prevents dust from entering the vacuum chamber through the bag opening, which is a few millimeters high and located between the sealing bars, during the evacuation process and contaminating the sealing seams as well as the vacuum chamber.
The essentially dust-free core panels are heated to temperatures around 150° C., then wrapped with a vacuum-tight high-barrier film, placed in a vacuum chamber and evacuated. The remaining opening of the high-barrier film bag is located between two sealing bars. At the end of the evacuation process, the two sealing bars are pressed against one another and seal the bag opening by the effect of the heat. After the ventilation of the vacuum chamber, the atmospheric air pressure presses on the evacuated insulation panels.
Core panels of microporous silica powders exhibit a very fine pore structure and permit relatively high gas pressures without the thermal conductivity of the remaining gas playing a role. Thus, with these microporous materials, only a vacuum of 1 to 10 mbar is required in order to bring the thermal conductivity to 0.004 to 0.005 W/mK. Wrappings made of special high-barrier films, which have only a very thin, vaporized aluminum coating, ensure that the gas pressure in the core material rises only one mbar per year. However, the production process described above for the microporous silica powder and the complex pressing process for the powder panels means a relatively high price for the core material. In the production of thermal insulation panels, the core is usually cut or sawn out of large sheets of the compressed core material. This sort of cut-out leaves inevitable remainders, which must be disposed of as scrap and thus further add to the cost of the production method. The thickness of thermal insulation panels produced in this way is predetermined by the thickness of the sheets of the raw material and therefore cannot be altered. No forms other than panel-shaped can be produced with this known method.